I am sure Greenpeace felt very proud of themselves when they locked themselves inside a Central Plains Water irrigation pipe to "protest dairy intensification".

They shouldn't be. Quite apart from putting themselves at risk on a dangerous construction site, breaking the law and tying up police time, they were wrong on a number of counts.

The first problem with the Greenpeace protest was the idea that irrigation schemes like Central Plains Water automatically lead to more dairy intensification. This is not true. The new farms connecting to Central Plains Water are traditional mixed cropping farms. The same holds true for other new irrigation developments like the Hurunui Water Project in North Canterbury, the North Otago Irrigation Company and Hunter Downs in South Canterbury. Across the country, around 50 percent of irrigated land has other uses – growing food, raising sheep and beef cattle, and for wineries.

The other assumption made by Greenpeace is that dairy farming automatically leads to water pollution. Even if a mixed cropping farmer in Selwyn did decide to convert to dairy, they now face strict new farm nutrient limits. These came into force last year through the Canterbury Land and Water Regional Plan. The plan sets out the strict controls and monitoring requirements for all farmers – including nutrient leaching limits, water use efficiency standards and fencing of waterways.

This will see Canterbury's lowland streams cleaned up over time. There are already over 3000 farms with Farm Environment Plans, which set out how they will meet the new controls. These are independently audited. Any farm found wanting must make changes – or face enforcement action.

It's ironic that the new investment in irrigation Greenpeace is against is actually the thing that brings the environmental improvements they want. Changing technology is already resulting in huge improvements in water efficiency. The majority of farms have invested in precision technology to monitor and apply water – an ECan and IrrigationNZ joint study in 2016 showed 70 per cent of farms now have this technology, compared to 20 per cent five years ago.

Taking less water allows improved river and lake flows, reduced run off and leaching and more water for fish. Modernisation of existing infrastructure – piping and implementation of automated control systems – typically results in around 20 per cent less water being used.

Which leads us to some of the historic problems we're facing, and how irrigation can help.

As an example, in the Selwyn catchment there is an historic over-allocation of groundwater. What Central Plains does is switch existing groundwater users to stored alpine water. This reduces over allocation, improves flows in lowland streams and the water quality in the lake. In the first two seasons of Central Plains operation, 60 million cubic meters of groundwater which had consent to be drawn from aquifers were not taken because alpine water was available for farmers. And 45 million cubic metres of water will also be introduced to the Selwyn River in the future to enhance flows in lowland streams and Lake Ellesmere/Te Waihora.

Should stricter environmental regulations relating to irrigation have been put in place earlier? Yes, I think they should have been. Have the benefits been realised yet from the stricter regulations now operating in Canterbury? No, they haven't. It will take time for those benefits to be seen, but we will see them. And the new regulations are costing farmers and growers a lot in time, money and effort, to meet them. This will hurt but it will be a beneficial investment over time.

And now, on top of that, irrigators are potentially facing a water tax. As its currently proposed, the tax will take away around $40 million every year from the 6000 irrigators in Canterbury. Over ten years that's $400 million being taken away from investment in water use efficiency – an action key to cleaning-up our rivers. Another issue with the tax is that Labour wants to spend it fencing off waterways, when this is now a legal requirement on farmers in Canterbury, many of whom have already done it.

Instead of doing their best to further deepen the urban-rural divide, through an exclusive focus on rural water quality issues, Greenpeace should bring some attention to urban problems. According to the Ministry for the Environment our least swimmable rivers are located in Auckland, where 62 per cent of rivers are poor for swimming and none are good or excellent. The Avon and the Heathcote are among the most polluted in Canterbury because Christchurch city continues to have issues with illegal sewage discharges.

Pipe protester Rosemary Penwarden threw around the figure of 34,000 Cantabrians a year getting sick from waterborne illness – which we can't find a source for – StatsNZ say there were only 8600 cases in the whole country in 2014 – but they didn't mention how many were from town water problems.

So should Greenpeace actually be chaining themselves to sewage pipes in the Avon and Heathcote estuaries?

Very possibly. They won't, though, because it wouldn't fit with their position that irrigation and dairy farming are the source of all our problems. It is a seductively simple equation to a complex issue, and it is simply not true.